This chart shows the evolution over time of the distribution across income groups of the share of confirmed cases in the the global total. Because confirmed cases and confirmed fatalities rely on testing, there is a strong similarity between this chart and the one on the shifting mortality distribution.
High-income countries account for the highest share in global confirmed cases. There are a number of reasons why one might expect highly urbanized and well-connected settings to be more susceptible to the spread of COVID-19. At the same time, physical distancing may be difficult to accomplish in developing countries with high rates of poverty and informality.
There are obviously many factors at work, but the extent and quality of testing are also likely to play an important role. Indeed, if other factors were constant, one would expect high-income countries to account for a larger share in confirmed cases globally simply because they tend to test more.